For log4net to work, the log4net.config file needs to be copied into the TestResult folder created by Visual Studios testrunner. In order to achieve this, enter the “Test” menu in VS, select “Edit Test Run Configurations”, “Deployment” and there, add your log4net.config file.

This made things work for me.

Note: I’m using the built-in testrunner in Visual Studio to drive my tests and not NUnit right now.
Note2: The first thing I did was setting it up as I did in my previous post, I haven’t tried to see if just adding the file to deployment is enough, it might not be.